Re: [PATCH v4 1/5] mtd: rawnand: meson: fix command sequence for read/write

[Miquel Raynal]

Hi Arseniy,

avkrasnov@xxxxxxxxxxxxxx wrote on Wed, 24 May 2023 12:05:47 +0300:

> On 23.05.2023 12:12, Arseniy Krasnov wrote:
> > Hello Miquel, Liang
> > 
> > On 22.05.2023 18:05, Miquel Raynal wrote:  
> >> Hi Arseniy,
> >>
> >> AVKrasnov@xxxxxxxxxxxxxx wrote on Mon, 15 May 2023 12:44:35 +0300:
> >>  
> >>> This fixes read/write functionality by:
> >>> 1) Changing NFC_CMD_RB_INT bit value.  
> >>
> >> I guess this is a separate fix
> >>  
> > 
> > Ok, I'll move it to separate patch
> >   
> >>> 2) Adding extra NAND_CMD_STATUS command on each r/w request.  
> >>
> >> Is this really needed? Looks like you're delaying the next op only. Is
> >> using a delay enough? If yes, then it's probably the wrong approach.  
> 
> Hi Miquel, small update, I found some details from @Liang's message in v1 talks from the last month:
> 
> *
> After sending NAND_CMD_READ0, address, NAND_CMD_READSTART and read status(NAND_CMD_STATUS = 0x70) commands, it should send
> NAND_CMD_READ0 command for exiting the read status mode from the datasheet from NAND device.

That is true.

> but previous meson_nfc_queue_rb()
> only checks the Ready/Busy pin and it doesn't send read status(NAND_CMD_STATUS = 0x70) command.
> i think there is something wrong with the Ready/Busy pin(please check the hardware whether this
> Ready/Busy pin is connected with SOC) or the source code. i have the board without Ready/Busy pin and prefer to use the
> nfc command called RB_IO6. it sends NAND_CMD_STATUS command and checks bit6 of the status register of NAND device from the
> data bus and generate IRQ if ready.
> *
> 
> I guess, that sequence of commands from this patch is described in datasheet (unfortunately I don't have it and relied on the old driver).
> Yesterday I tried to remove sending of NAND_CMD_STATUS from this patch, but it broke current driver - i had ECC errors, so it looks like
> "shot in the dark" situation, to understand this logic.

When an operation on the NAND array happens (eg. read, prog, erase),
you need to wait "some time" before accessing the internal sram or even
the chip which is "busy" until it gets "ready" again. You can probe the
ready/busy pin (that's the hardware way, fast and reliable) or you can
poll a status with NAND_CMD_STATUS. The chips are designed so they can
actually process that command while they are doing time consuming tasks
to update the host. But IIRC every byte read will return the status
until you send READ0 again, which means "I'm done with the status
read" somehow.

Please see nand_soft_waitrdy() in order to understand how this is
supposed to work. You can even use that helper (which is exported)
instead of open-coding it in your driver. See atmel or sunxi
implementations for instance.

As using the native RB pin is better, you would need to identify
whether you have one or not at probe time and then either poll the
relevant bit of your controller if there is one, or fallback to the
soft read (which should fallback on exec_op in the end).

Thanks,
Miquèl